Today, solar wafers are traced until finishing the solar cell using either a difficult technique to mark the wafer at an edge or applying a so called virtual serialization. In case of virtual serialization, the traceability is often lost after the cell is finished and moved to a module assembly. However, for reason of process control as well as quality control there is a need for a trace of the wafers during the production process as well as after finishing the cell assembly. Such trace would enable to identify e.g. defect cells, trace back the production of such cells up to the very beginning, and to systematically identify sources of errors in the production.
US20090073440 A1 discloses a feature of reading a surface profile (i.e. fingerprint) of a wafer at a spot on the wafer using a contact-free reading technique (e.g. using laser technique). Thereafter, current surface profile is compared with the immediately preceding surface profile. It discloses a method for inspecting a surface of a semiconductor workpiece, the method comprising: providing a surface inspection system and using the surface inspection apparatus to cause laser light to impinge upon a test location on the workpiece surface and thereby cause the laser light to emerge from the surface as returned light comprising at least one of reflected light and scatter light; collecting the returned light and generating a signal from the returned and collected light, the signal comprising a signal value representative of a feature of the workpiece surface at the test location; providing a plurality of threshold candidates and causing the surface inspection system to select a threshold from among the plurality of threshold candidates; comparing the threshold to the signal value to obtain a difference value; using the difference value to assess the feature of the workpiece surface at the test location; and using the surface inspection system to automatically cause the method to be repeated for a plurality of test locations on the workpiece surface.
U.S. Pat. No. 5,537,325 discloses an apparatus and method for the identification of semiconductor wafers in a production process of such. Here, when an ingot is sliced into wafers, they are given serial numbers for identification. This makes possible to identify which any wafer being processed is of those sliced from the ingot no matter where the wafer is in a manufacturing process. Each wafer is traced so as to determine the path along which the wafer was transferred during the manufacturing process, and results are stored as wafer information.
U.S. Pat. No. 6,447,370 B1 discloses a method of presenting a wafer to a metrology device for measuring surface characteristics of the wafer. In accordance with one aspect of the present invention, the metrology device is physically integrated with the wafer processing machine between two wafer processing stations. The metrology device measures the uniformity and or thickness of the wafer. In the preferred embodiment, the measuring device is a single wavelength multi-angle reflectometry device. The device comprises a light source provided from multiple emission points. In the preferred embodiment, the light source comprises a laser and the emission point comprises fiber optic cabling. In accordance with yet another aspect of this patent, a wafer location means is provided to track the position of the wafer passing over the wafer measurement device. Preferably, the tracking device comprises a light curtain comprising a light beam which detects when the wafer is entering the measuring device and suitably enables the tracking of the location of the wafer.
US 2008/0279442 discloses an inspection apparatus configured to measure a property of a substrate. The inspection apparatus includes a first radiation source configured to irradiate a measurement spot on a patterned target of a substrate; a second radiation source configured to irradiate an area of the patterned target that is larger than the measurement spot; a first detector configured to detect radiation having been diffracted from the measurement spot and radiation having been reflected from the area of the patterned target, and to output an image of the relative positions of the measurement spot and the area of the patterned target; an image processor configured to receive the output of the first detector, to compare the position of the measurement spot with respect to the area of the patterned target, and to output a value of the position of the measurement spot relative to the area of the patterned target; a second detector configured to detect radiation from the first radiation source having been diffracted from the measurement spot, and to output a diffraction spectrum corresponding to the patterned target; and a processor configured to process the output of the image processor and the output of the second detector to reconstruct the pattern of the patterned target within the measurement spot.